Does the Starting battery also need to be wired behind the Victron BMV-602S shunt?

CapTim · #1 (**permalink**) 09-09-2011

Hello! Here's another wiring question for you experts...

I'm redoing the wiring on my new-to-me 35 year old boat. Part of that is the battery banks, and part of that is installing a battery monitor. I've settled on the Victron BMV-602S, as it is nicely priced, is apparently easy to install, and does the job it needs to do with a minimum of fuss.

So. It's clear that there can be no loads behind the shunt on the negative battery terminal of the house battery. (By behind I mean, of course, refers to the battery side, not the 'rest-of-the-boat' side).

However, don't I want to connect the negative post on the start bank to the negative post on the house bank? And if so, do I make that connection on the boat side of the shunt or on the house bank side?

In a related question, where does the 'ship ground' go? I assume the 'ship ground' is going to be the engine in most cases, right?

My concern would be that if I connect the ship ground behind the shunt, and then some other piece of electrical equipment also is grounded to the ship ground, then that load would not be monitored by the Battery Monitor, right?

So, to recap, two questions:

1) _If_ I'm supposed to connect the negative side of both banks together, do I connect them ahead of the shunt or behind it?

2) _If_ I'm supposed to connect one or both battery banks to the ship ground (engine?), do I connect them ahead of the shunt or behind it?

Thanks for all the help!

mitiempo · #2 (**permalink**) 09-09-2011

The house bank's negative connection goes to the shunt first. Any connection to any equipment or the engine block is after the shunt. After the shunt I would install a bus for the house negative, start battery negative, and from there go to the block. Do not wire the start battery negative behind the shunt.

Here is a diagram from the manual showing how the start battery is wired with the BMV-602 so it will read voltage of the start battery.

CapTim · #3 (**permalink**) 09-09-2011

Excellent! That's exactly what I needed... Thanks Brian!

Maine Sail · #4 (**permalink**) 09-09-2011

Yes the start battery should go on the "load" side of the shunt not the battery side. If the banks are combined via a parallel switch of BOTH feature you WANT that outflow or inflow of current from the lower or higher charged bank to be read.

When you "combine" banks of different charge levels current flows in or out between them until they "equalize" and the current stops flowing. The only way to read this is to wire the start/reserve battery to the load side of the shunt.

CapTim · #5 (**permalink**) 09-09-2011

Quote:

Originally Posted by Maine Sail

When you "combine" banks of different charge levels current flows in or out between them until they "equalize" and the current stops flowing. The only way to read this is to wire the start/reserve battery to the load side of the shunt.

Ahh.. that was the part I was missing in my head. Well, that and the diagram from Brian!

mitiempo · #6 (**permalink**) 09-09-2011

On the other hand if you use your house bank for house loads and engine starting you can leave the other battery as an "emergency" battery. This battery can be wired to the bus after the shunt and Victron's diagram I posted is the proper way to wire it. The BMV-602 will read the start/emergency battery voltage which is all you need to know. With this exception the data on the Victron relates to the house bank, which is the one you need the info on. There would not be any need to ever combine the battery banks. If the house bank was not enough to start the engine the emergency battery by itself will do the job.